Ultrasonic wave transmitter/receiver

ABSTRACT

An ultrasonic wave transmitter/receiver is provided in which the transmission/reception range thereof in at least one direction is relatively narrow, and which has stable reverberation characteristics. When the thickness of a thick-walled portion is t1, the thickness of each of thin-walled portions is t2, the thickness of a side portion provided continuously with the thin-walled portion is A, x=t2/t1, and y=A/t2, this ultrasonic wave transmitter/receiver is formed so that x and y are within the range defined by the following equations:  
     0.50≦ x ≦0.64  
     0.75≦ y ≦1.75  
     y≦−(50/7)· x +163/28  
     y≧−(50/7)· x +135/28

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an ultrasonic wavetransmitter/receiver used as, for example, a clearance sensor and a backsensor for use in automobile.

[0003] 2. Description of the Related Art

[0004] Hitherto, an ultrasonic wave transmitter/receiver is known inwhich a piezoelectric vibrating element is fixed on the inner bottomsurface of a cylindrical case with a bottom, and which uses the outerbottom surface of the case as an ultrasonic wave transmitting/receivingsurface. When using such an ultrasonic wave transmitter/receiver as asensor for use in a car, if the transmission/reception range in thevertical direction is too wide with respect to the ground, reflectedwaves from the ground are detected as noises, and if thetransmission/reception range in the horizontal direction is too narrow,the detection range has a blind spot. Neither of these is desirable.Accordingly, an ultrasonic wave transmitter/receiver has been inventedwhich is arranged so that its transmission/reception range in thevertical direction is narrow and so that its transmission/receptionrange in the horizontal direction is wide, by forming the hollow portionof the case so as to be long in the vertical direction and short in thehorizontal direction, and further by forming a thick-walled portion andthin-walled portions on the bottom of the case. In such an ultrasonicwave transmitter/receiver, for example, by forming a thick-walledportion with a thickness of 0.75 mm and thin-walled portions with athickness of 0.3 mm on the case bottom with a diameter of 18 mm, and bydisposing the thin-walled portions in the vertical direction, anultrasonic wave transmitter/receiver wherein the transmission/receptionrange in the vertical direction is 40°, can be obtained.

[0005]FIG. 9 shows an example of an ultrasonic wave transmitter/receiver1 used as a back sensor for use in a car. The transmission/receptionrange is expressed by a full angle at half maximum. The “full angle athalf maximum” refers to an angle formed by both directions at which areduction of 20·log 0.5 dB (about 6 dB) in the transmission/receptionsensitivity occurs with respect to the transmission/receptionsensitivity in the direction opposite to the bottom (the direction of0°).

[0006] However, in such a conventional ultrasonic wavetransmitter/receiver, since the reverberation characteristics areunstable and the reverberation time is long, ultrasonic waves reflectedfrom an object adjacent to the ultrasonic wave transmitter/receiver caninterfere with the reverberation thereof, so that there are cases wherethe existence of the adjacent object cannot be detected and/or where thedistance to the adjacent body cannot be measured. In particular, whenwater drops are adhered on the transmitting/receiving surface, thereverberation time is prone to be longer, and hence, a problem occurswhen using this ultrasonic wave transmitter/receiver as a sensor for usein a car, the sensor being exposed to wind and rain.

SUMMARY OF THE INVENTION

[0007] Accordingly, it is an object of the present invention to providean ultrasonic wave transmitter/receiver in which thetransmission/reception range thereof in at least one direction isrelatively narrow, and which has stable reverberation characteristics.

[0008] In accordance with the present invention, there is provided anultrasonic wave transmitter/receiver which comprises a cylindrical casewith a bottom, a piezoelectric vibrator fixed on the inner bottomsurface of the bottom of the case, and an ultrasonic wavetransmitting/receiving surface defined by the outer bottom surface ofthe bottom of the case. In this ultrasonic wave transmitter/receiver,the bottom of the case includes a thick-walled portion on which thepiezoelectric vibrator is fixed, and a thin-walled portion thinner thanthe thick-walled portion. When the thickness of the thick-walled portionis t1, the thickness of the thin-walled portion is t2, the thickness ofa side portion provided continuously with the thin-walled portion is A,and the equations are set as x=t2/t1, and y=A/t2, this ultrasonic wavetransmitter/receiver is formed so that x and y are within the rangedefined by the following equations:

0.50≦x≦0.64

0.75 ≦y≦1.75

y≦−(50/7)·x+163/28

y≧−(50/7)·x+135/28

[0009] The above and other objects, features, and advantages of thepresent invention will be clear from the following detailed descriptionof the preferred embodiments of the invention with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a diagrammatic sectional view showing an ultrasonic wavetransmitter/receiver in accordance with an embodiment of the presentinvention;

[0011]FIG. 2A is a cross sectional view illustrating an example of acase of the ultrasonic wave transmitter/receiver shown in FIG. 1, thecase being taken along a plane parallel with the bottom surface thereof;and FIG. 2B is a vertical section showing the case taken along a lineb-b in FIG. 2A;

[0012]FIG. 3 is a diagram showing the relationship between t2/t1 and thefull angle at half maximum when A/t2 is varied;

[0013]FIG. 4 is a diagram showing the relationship between t2/t1 and thereverberation time when A/t2 is varied;

[0014]FIG. 5 is a diagram showing the relationship between A/t2 and thefull angle at half maximum when t2/t1 is varied;

[0015]FIG. 6 is a diagram showing the relationship between A/t2 and thereverberation time when t2/t1 is varied;

[0016]FIG. 7 is a diagram showing a desirable range of numeric valueswhen x=t2/t1, and y=A/t2;

[0017]FIG. 8 is a diagram showing the transmission/reception sensitivityof ultrasonic wave transmitter/receivers;

[0018]FIG. 9 is a diagrammatic view showing the detection range of aback sensor for use in a car; and

[0019]FIG. 10 is a diagram showing the relationship between the fullangle at half maximum and the detection distance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020]FIG. 1 is a sectional view showing an ultrasonic wavetransmitter/receiver in accordance with an embodiment of the presentinvention. This ultrasonic wave transmitter/receiver 10 includes asubstantially cylindrical case 12. The case 12 is, for example, made ofaluminum. On the inner bottom of the case, a thick-walled portion 14 andthin-walled portions 16 are formed. A piezoelectric vibrating element 18is fixed on the thick-walled portion 14 in the inner bottom of the case12. One electrode of the piezoelectric vibrating element 18 is connectedto the case which is grounded. A sound absorbing material 20 is disposedon the opposite side to inner bottom surface of the case 12 with thepiezoelectric vibrating element 18 therebetween.

[0021] A capacitor 22 is disposed opposite to the piezoelectricvibrating element 18 across the absorbing material 20. Fixation members24 constituted of silicone rubber or the like are each fitted to bothends of the capacitor 22. One electrode of the capacitor 22 and theother electrode of the piezoelectric vibrating element 18 areelectrically connected by a lead 26. An external terminal 28 isconnected to the one electrode of the capacitor 22. The other electrodeof the capacitor 22 is connected to the case which is grounded, by alead (not shown). Also, an external terminal (not shown) is provided onthe case 12.

[0022] The inner bottom of the case 12 is filled with a first adhesive30 such as a silicone-based adhesive having a relatively high viscosity.The first adhesive covers the sound absorbing material 20 and thepiezoelectric vibrating element 18. The purpose of using an adhesivehaving a high viscosity, is to minimize the influences of the adhesiveimpregnated into sound absorbing material upon the acousticcharacteristics. After the first adhesive 30 has been cured, thefixation members 24 on both sides of the capacitors 22 are placedthereon. Furthermore, a second adhesive 32 such as a silicone-basedadhesive having a relatively low viscosity is filled thereover. Thereason for using an adhesive with a low viscosity as the secondadhesive, is to facilitate the filling work.

[0023]FIG. 2A is a cross sectional view illustrating an example of thecase 12 of the ultrasonic wave transmitter/receiver 10 shown in FIG. 1,the case being taken along a plane parallel with the bottom thereof, andFIG. 2B is a vertical section showing the case taken along a line b-b inFIG. 2A. As shown in FIG. 2A, a hollow portion of the case 12 is formedinto, for example, a substantially oval shape in a plan view. In thedirection of the long axis of the oval, the thin-walled portions 16thinner than the thick-wall portion 14 are formed on both sides of thethick-wall portion 14. On the other hand, the thick-wall portion 14 isformed so as to extend in the direction of the short axis of the oval.The ultrasonic wave transmitter/receiver 10 shown in FIG. 1 is used sothat the direction of the long axis of the cross section of the case 12is set in the direction vertical with respect to the ground, and theshort axis thereof is set in the direction horizontal with respect tothe ground. In the ultrasonic wave transmitter/receiver 10, the outerbottom surface of the case 12 defines a transmitting/receiving surface.Here, the shape of the cross section of the case 12 is not limited tosubstantially oval shape, but the cross section thereof may be formedinto a substantially rectangular shape, a substantially elliptic shape,or a substantially circular shape.

[0024] By varying the thickness of the thick-walled portion 14, each ofthe thin-walled portions 16, and the side portion 12 a providedcontinuously with the thin-walled portions 16, of the case shown in FIG.2, full angles at half maximum and reverberation times of the ultrasonicwave transmitter/receiver 10 using these cases 12 were measured. Themeasurement results are shown in Tables 1 to 10, and FIGS. 3 to 6. Here,the case 12 used in this embodiment is entirely formed of aluminum andhave a diameter of 18 mm. TABLE 1 A/t2 = 0.75 t2/t1 0.43 0.50 0.57 0.640.71 Full angle at half AVE 29 32 35 38 41 maximum (°) Reverberationtime AVE 2.18 1.56 1.35 1.22 1.07 (ms) MAX 2.40 1.75 1.50 1.35 1.15 MIN2.05 1.45 1.25 1.15 1.00

[0025] TABLE 2 A/t2 = 1.00 t2/t1 0.43 0.50 0.57 0.64 0.71 Full angle athalf AVE 30 33 36 39 42 maximum (°) Reverberation time AVE 2.15 1.531.32 1.19 1.07 (ms) MAX 2.35 1.70 1.45 1.30 1.15 MIN 2.00 1.40 1.20 1.101.00

[0026] TABLE 3 A/t2 = 1.25 t2/t1 0.43 0.50 0.57 0.64 0.71 Full angle athalf AVE 31 34 37 40 43 maximum (°) Reverberation time AVE 2.12 1.501.29 1.17 1.07 (ms) MAX 2.30 1.65 1.40 1.30 1.15 MIN 1.95 1.35 1.15 1.101.00

[0027] TABLE 4 A/t2 = 1.50 t2/t1 0.43 0.50 0.57 0.64 0.71 Full angle athalf AVE 32 35 38 41 44 maximum (°) Reverberation time AVE 2.10 1.481.27 1.15 1.07 (ms) MAX 2.25 1.60 1.35 1.25 1.15 MIN 1.90 1.30 1.10 1.051.00

[0028] TABLE 5 A/t2 = 1.75 t2/t1 0.43 0.50 0.57 0.64 0.71 Full angle athalf AVE 33 36 39 42 45 maximum (°) Reverberation time AVE 2.08 1.461.25 1.14 1.07 (ms) MAX 2.25 1.60 1.35 1.25 1.15 MIN 1.90 1.30 1.10 1.051.00

[0029] TABLE 6 t2/t1 = 0.43 A/t2 0.75 1.00 1.25 1.50 1.75 Full angle athalf AVE 29 30 31 32 33 maximum (°) Reverberation time AVE 2.25 2.201.97 1.84 1.72 (ms) MAX 2.60 2.35 2.10 1.90 1.75 MIN 2.00 2.00 1.90 1.801.70

[0030] TABLE 7 t2/t1 = 0.50 A/t2 0.75 1.00 1.25 1.50 1.75 Full angle athalf AVE 32 33 34 35 36 maximum (°) Reverberation time AVE 1.85 1.801.49 1.38 1.32 (ms) MAX 2.20 1.95 1.60 1.40 1.35 MIN 1.60 1.60 1.40 1.351.30

[0031] TABLE 8 t1/t2 = 0.57 A/t2 0.75 1.00 1.25 1.50 1.75 Full angle athalf AVE 35 36 37 38 39 maximum (°) Reverberation time AVE 1.45 1.351.14 1.02 1.02 (ms) MAX 1.70 1.45 1.20 1.05 1.05 MIN 1.20 1.20 1.10 1.001.00

[0032] TABLE 9 t2/t1 = 0.64 A/t2 0.75 1.00 1.25 1.50 1.75 Full angle athalf AVE 38 39 40 41 42 maximum (°) Reverberation time AVE 1.37 1.291.09 1.02 1.02 (ms) MAX 1.65 1.40 1.15 1.05 1.05 MIN 1.15 1.15 1.05 1.001.00

[0033] TABLE 10 t2/t1 = 0.71 A/t2 0.75 1.00 1.25 1.50 1.75 Full angle athalf AVE 41 42 43 44 45 maximum (°) Reverberation time AVE 1.35 1.271.07 1.02 1.02 (ms) MAX 1.65 1.40 1.10 1.05 1.05 MIN 1.15 1.15 1.05 1.001.00

[0034] Next, Table 11 and FIG. 10 show the relationship between the fullangle at half maximum and the detection distance in the verticaldirection, with an installation height of 40 cm set, when the ultrasonicwave transmitter/receiver 10 is used as a back sensor for use in a caras shown in FIG. 10. TABLE 11 Full angle at half maximum (°) 40 50 60 7080 Detection distance (cm) 110 85 70 60 50

[0035] As can be seen from Table 11 and FIG. 10, the smaller the fullangle at half maximum is, the longer the detection distance is.Particularly, the detection distance in a case where the full angle athalf maximum is 40° is 1.5 times as long as that in a case where thefull angle at half maximum is 60°. However, in this ultrasonic wavetransmitter/receiver 10, since the transmitting/receiving surface servesas both a transmitting surface and a receiving surface for ultrasonicwaves, unless the vibrations when ultrasonic waves are transmitted areisolated in a time as short as possible, reflected waves will be buriedin the vibrations when transmitted, and will inhibit the ultrasonic wavetransmitter/receiver from performing a detection. Hence, it ispractically required, in addition to that the full angle at half maximumis small, that the reverberation time is not more than 1.5 ms under theconditions that water drops are adhered to the transmitting/receivingsurface. If the reverberation time is not more than 1.5 ms with waterdrops adhered to the transmitting/receiving surface, a lessreverberation time will be obtained under the dry conditions.

[0036] Accordingly, from the above results, the conditions whichsimultaneously meet the properties that the full angle at half maximumis not more than 40°, and that the reverberation time is not more than1.5 ms, are shown in Table 12. TABLE 12 t2/t1 0.43 0.50 0.57 0.64 0.71A/t2 0.75 ◯/ ◯/ ◯/◯ ◯/◯ /◯ 1.00 ◯/ ◯/ ◯/◯ ◯/◯ /◯ 1.25 ◯/ ◯/◯ ◯/◯ ◯/◯ /◯1.50 ◯/ ◯/◯ ◯/◯ /◯ /◯ 1.75 ◯/ ◯/◯ ◯/◯ /◯ /◯

[0037] In order to achieve the effects intended by the presentinvention, as can be seen from Table 12, when the ratio of the thicknesst2 of the thin-walled portion 16 with respect to the thickness t1 of thethick-walled portion 14 is 0.57, it is desirable that the ratio of thethickness A of the side portion 12 a with respect to the thickness t2 ofthe thin-walled portion 16 be set to 0.75 to 1.75.

[0038] When the ratio of the thickness t2 of the thin-walled portion 16with respect to the thickness t1 of the thick-walled portion 14 is 0.50,it is desirable that the ratio of the thickness A of the side portion 12a with respect to the thickness t2 of the thin-walled portion 16 be setto 1.25 to 1.75.

[0039] Also, when the ratio of the thickness t2 of the thin-walledportion 16 with respect to the thickness t1 of the thick-walled portion14 is 0.64, it is desirable that the ratio of the thickness A of theside portion 12 a with respect to the thickness t2 of the thin-walledportion 16 be set to 0.75 to 1.25.

[0040] From these results, the relationship shown in FIG. 7 are induced.That is, when x=t2/t1, and y=A/t2, the thickness t1 of the thick-walledportion 14, the thickness t2 of each of the thin-walled portions 16, andthe thickness A of the side portion 12 a are set so that x and y arewithin the range defined by the following equations, whereby the effectsintended by the present invention can be achieved.

0.50≦x≦0.64  (1)

0.75 ≦y≦1.75  (2)

y≦−(50/7)·x+163/28  (3)

y≧−(50/7)·x+135/28  (4)

[0041] In FIG. 8, the solid lines show the directivity characteristicsin the vertical and horizontal directions of the ultrasonic wavetransmitter/receiver 10 in accordance with an embodiment using analuminum case wherein the diameter is 18 mm, the thickness t1 of thethick-walled portion 14 is 0.70 mm, the thickness t2 of each of thethin-walled portions 16 is 0.40 mm, and the thickness A of the sideportion 12 a provided continuously with the thin-walled portions is 0.4mm.

[0042] Also, in FIG. 8, the broken lines show the directivitycharacteristics in the vertical direction of the ultrasonic wavetransmitter/receiver 10 in accordance with a comparative example usingan aluminum case wherein the diameter is 18 mm, the thickness t1 of thethick-walled portion is 0.70 mm, the thickness t2 of each of thethin-walled portions is 0.30 mm, and the thickness A of the side portion12 a provided continuously with the thin-walled portion is 0.4 mm.

[0043] It is obvious from FIG. 8 that the full angle at half maximum(approximately 30°) of the ultrasonic wave transmitter/receiver 10 inaccordance with the embodiment of the present invention providessuperior directivity characteristics in the vertical direction to thefull angle at half maximum (approximately 60°) of the conventionalexample.

[0044] Thus, in accordance with the ultrasonic wave transmitter/receiver10 of this embodiment, since the full angle at half maximum in thevertical direction is not more than 40°, the detection distance can bemade longer, and is hardly subjected to influences of reflected wavesfrom the ground. Furthermore, in accordance with the ultrasonic wavetransmitter/receiver 10 of this embodiment, since the reverberation timeis not more than 1.5 ms when water drops are adhered to thetransmitting/receiving surface, the influence of transmission waves uponreflected waves can be minimized.

[0045] As is evident from the foregoing, in accordance with the presentinvention, an ultrasonic wave transmitter/receiver is provided in whichthe transmission/reception range thereof in at least one direction isrelatively narrow, and which has stable reverberation characteristics.This ultrasonic wave transmitter/receiver has a long detection distance,and can be used as a back sensor having a superior performance.

[0046] While the present invention has been described with reference towhat are at present considered to be the preferred embodiments, it is tobe understood that various changes and modifications may be made theretowithout departing from the invention in its broader aspects andtherefore, it is intended that the appended claims cover all suchchanges and modifications as fall within the true spirit and scope ofthe invention.

What is claimed is:
 1. An ultrasonic wave transmitter/receiver,comprising: a cylindrical case having a bottom; a piezoelectric vibratorfixed on the inner bottom surface of the bottom of said case; anultrasonic wave transmitting/receiving surface defined by the outerbottom surface of the bottom of said case; said bottom of said caseincluding a thick-walled portion on which said piezoelectric vibrator isfixed, and a thin-walled portion thinner than said thick-walled portion;and when the thickness of said thick-walled portion is tl, the thicknessof said thin-walled portion is t2, the thickness of a side portionprovided continuously with said thin-walled portion is A, and theequations are set as x t2/t1, and y=A/t2, said ultrasonic wavetransmitter/receiver being formed so that x and y are within the rangedefined by the following equations: 0.50≦x≦0.64 0.75 ≦y≦1.75y≦−(50/7)·x+163/28 y≧−(50/7)·x+135/28